Devices for transcutaneous electrical stimulation of nerves are described in international patent applications WO2006/054118 and WO2010/070332. The second of these describes a device including a flexible substrate on which are mounted positive and negative electrodes; a power supply connectable to the electrodes; and control means for activating the electrodes. The preferred embodiment of the device is in the form of an elongate “tongue” of flexible plastic which carries the electrodes (this is shown in FIG. 14 of WO2010/070332, reproduced here as FIG. 1). The device is intended for use in stimulating a nerve in the leg (specifically, the lateral and/or medial popliteal nerve) which innervates opposed leg muscles so as to cause isometric contraction of the muscles. This serves to activate the calf blood pump to encourage blood circulation in the patient. The device is intended for use in reducing the incidence of DVT, or for various other treatments (eg, enhancement of bone marrow perfusion, sports training and rehabilitation, peripheral arterial disease, among others). However, it will be apparent to the skilled person that this, and other similar devices, may be used to stimulate other areas of the body.
A key stage in using the device correctly is identifying the correct location for nerve stimulation. If the device is placed on the body incorrectly, then there may be reduced or even no stimulation of the correct nerve, such that the device will fail to operate as intended. In many patients it is relatively easy to identify the correct location for placement, since in general the position for optimum stimulation of the lateral or medial popliteal nerve will vary little between individuals. However there is of course some variation, and in some patients it may be more difficult to locate the correct position, or the correct position may differ more markedly from the norm. Accordingly, it would be desirable to have some way in which the location for nerve stimulation may be identified for using the device.
The device as described in WO2010/070332 and reproduced herein as FIG. 1 is not intended to be reusable. A preferred embodiment includes a layer of hydrogel or other electrically conductive gel which is located between the electrodes and the user's skin. The gel both provides electrical contact between the electrodes and the user, but also serves to adhere the device to the user. Moving and repositioning the device (for example, to identify the optimal location for nerve stimulation) would rapidly degrade the gel to the point that adhesion would be lost, and possibly also electrical contact. It is therefore not practical to identify the preferred location for the device simply by repeated moving and repositioning.
The patient could use two devices, one for identifying the correct location, which will allow the conductive gel to degrade, and a second working device for use once the correct location has been identified and marked. This approach is undesirable as it effectively discards one of the devices.
An alternative approach therefore may be to place an additional gel—for example, ultrasound gel—on the patient, thereby allowing easy repositioning and sliding of the device over the patient until the correct location has been identified. The correct location may be marked, and the ultrasound gel removed prior to the working device being put into position. However, this is complex and potentially messy, so is not preferred.
The present inventors have therefore designed a modified device which allows a single device to be used both for initially locating the preferred contact position on a patient, and for use as a working device.